1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device or a display device using a polycrystalline semiconductor layer obtained by laser annealing a non-single crystal semiconductor layer on a substrate.
2. Description of the Prior Art
A flat display device comprising a display element using a liquid crystal and organic electroluminescence as optical members is small-sized, thin and has low power consumption, and has been developed for practical use in the field of OA apparatus, AV apparatus and the like. A liquid crystal display (LCD) and an organic EL display of an active matrix type having a thin film transistor (TFT) formed on a substrate supporting a liquid crystal and EL as a switching element for controlling the timing of holding and writing image data in each pixel has become commonplace because of high display quality. In particular, a display of a driver built-in type has been developed in which a TFT is used as a switching element of each pixel and is also used for a driver to drive the switching element, and the driver is formed together with the switching element on the periphery of a display area where each pixel is arranged. Consequently, size and cost can be reduced still further.
For the display of a driver built-in type, a TFT using a polycrystalline semiconductor film, particularly, polysilicon (p-Si) as a channel layer is suitable because it can achieve an operating speed which is also applicable to a driver and has a low deposition temperature resulting in formation on an inexpensive glass substrate having low heat resistance. When the polysilicon is to be formed, amorphous silicon formed on the substrate is laser annealed so that crystallization can be performed with a support substrate temperature set to 400 to 600xc2x0 C. The TFT is formed using p-Si thus obtained. Using this method, a driver circuit can be fabricated on a non-alkaline glass substrate.
The amorphous silicon (a-Si) is laser annealed by using a laser irradiation apparatus. In the laser irradiation apparatus, an optical system shapes a pulse laser beam emitted from a laser oscillation source into a beam having a predetermined section, and the beam thus obtained is irradiated on an amorphous silicon film formed on a processed substrate. The laser beam to be shaped and irradiated on the silicon film is, for example, square, and more particularly has the form of a belt or line in which a length in a direction of a major axis is much greater than that in a direction of a minor axis. A stage of the laser irradiation apparatus to be mounted on the processed substrate having an a-Si film formed thereon is movable horizontally and vertically in a plane direction. The stage is moved horizontally or vertically so that a pulse laser beam is relatively scanned over the a-Si film formed on the processed substrate horizontally or vertically.
FIG. 1 shows an enlarged sectional structure of a TFT portion formed on the processed substrate at a laser. annealing step A gate electrode 11 of a TFT is formed on a substrate 10 such as a non- alkaline glass. A gate insulation film 12 is formed to cover the gate electrode 11 and an a-Si film 13a which is a film to be laser annealed is formed on the gate insulation film 12. When a pulse laser beam is irradiated on the a-Si film 13a to perform the laser annealing, the a-Si film 13a is polycrystallized to form a p-Si film 13.
FIG. 2 shows a sectional structure of the TFT formed by using the p-Si film 13 obtained by laser annealing. FIG. 3 shows a planar structure of the obtained TFT. FIGS. 1 and 2 show sections taken along the line Axe2x80x94A in FIG. 3.
The p-Si film 13 obtained by laser annealing the a-Si film 13a is subjected to patterning in the shape of an island across a portion above the gate electrode 11. A region positioned just above the gate electrode 11 in the island-shaped p-Si film 13 is a non-doped channel region CH. A LD (Lightly Doped) region LD which is doped with an impurity having a low concentration is formed on both sides of the non-doped channel region CH, and a source region S and a drain region D which are doped with an impurity having a high concentration are formed on the outside of the LD region LD. An interlayer insulation film 15 such as SiNx, SiO2 or the like is formed to cover an implantation stopper film 14 used as a mask when the p-Si film 13 and the LD region LD are to be formed. A source electrode 16 and a drain electrode 17 are formed on the interlayer insulation film 15, and are connected to the source region S and the drain region D through a contact hole CT formed in the interlayer insulation film 15, respectively.
In a display unit, for example an LCD, pixels re usually arranged in a matrix and TFTs for driving the pixels and wirings are correspondingly placed in horizontal and vertical scanning directions, respectively. Accordingly, when these display elements are usually placed on a rectangular substrate, the directions of a plurality of TFTs formed on the processed substrate, that is, extension directions of channel widths or channel lengths of the channel regions CH, are any of a horizontal scanning direction H and a vertical scanning direction V of the LCD with respect to a substrate plane. In other words, the directions of the channels of the TFT elements are parallel or perpendicular to each other. A direction of a line beam, that is, a side of the line beam, a side of the substrate and the like are held in the horizontal scanning direction H or the vertical scanning direction V.
FIG. 4 is a graph showing a relationship between an irradiation laser energy on the a-Si film 13a (an axis of abscissa) and a grain size of the p-Si film 13 formed at that time (an axis of ordinate). As the energy is increased, the grain size is also enlarged. If an energy value Eo with which a maximum grain size is obtained is exceeded, the grain size is rapidly reduced. Accordingly, the energy should be kept within a narrow range between Ed and Eu in order to obtain a predetermined grain size.
For this reason, if the irradiation energy of the line beam is slightly varied and moves out of the optimum range between Ed and Eu, crystallization cannot be performed fully so that a defective crystallization region R having a small grain size is generated on a certain region in the p-Si film 13.
A positional relationship between a layout of each circuit element for liquid crystal driving which is formed on a processed substrate, for example, and an irradiated pulse laser beam is usually set as shown in FIG. 5. In FIG. 5, a mother substrate 59 acting as the processed substrate has a plurality of regions forming an active matrix substrate used for a TFT LCD (six regions, each of which will be hereinafter referred to as an active matrix substrate 2). Each active matrix substrate 2 is subjected to various manufacturing steps so that pixels are formed in a matrix and a p-Si TFT to be connected to each pixel is formed in a region 43 of FIG. 5, resulting in a display area (hereinafter referred to as a display area 43). Driver sections 44 and 45 are formed around the display area 43. The driver sections 44 and 45 serve to drive the p-Si TFT of the display area 43 and utilize a p-Si TFT formed almost simultaneously with the formation of the p-Si TFT of the display area 43.
FIG. 5 shows a state in which an amorphous silicon (a-Si) film is formed in a necessary region of the mother substrate 59 and a line-shaped laser beam that causes an irradiated region LB to extend in the vertical scanning direction V is sequentially shifted and irradiated on the a-Si film in the horizontal scanning direction H to perform annealing. By such laser annealing, a-Si is polycrystallized so that a p-Si film constructing a channel region of the TFT is obtained.
Thus, the annealing is performed by irradiating the pulse laser beam while sequentially shifting a position of the pulse laser beam. Therefore, a direction of an edge of the region where the laser beam is irradiated is usually coincident with the direction of the sides of the processed substrate as shown in FIG. 5 It has been confirmed that the defective crystallization region R is easily generated in the direction of the edge of the region LB where the laser beam is irradiated. In particular, a direction of a major axis of the region LB orthogonal to the scanning direction of the beam which is coincident with the horizontal scanning direction H of the substrate is shown in FIG. 5.
For this reason, a relationship between the channel region of the TFT formed on the processed substrate and the defective crystallization region R is often set as shown in FIG. 3 For example, a TFT used for the drivers 44 and 45 or the like takes a slender shape having a channel width W of the channel region CH greater than a channel length L as shown in FIG. 3 in order to particularly enhance operating speed and driving capability. A TFT used for a TFT LCD or the like often has the direction of a channel width and that of a channel length which are coincident with the directions of the sides of the substrate as described above. With such a layout, the direction of a channel, that is, an extension of the channel width W and an extension of a major axis of the defective crystallization region R are parallel or perpendicular to each other as shown in FIG. 3.
FIG. 3, in the case where a defective crystallization region RL divides the channel region CH vertically, that is, a defective crystallization region RL is generated in the direction of the length of the TFT channel A part MN of a moving path in the channel region CH is occupied by the defective crystallization region RL to cause deterioration and a residual moving path MG does not overlap the defective crystallization region RL in the direction of the channel width Accordingly, a width of the moving path decreases so that a substantial channel width is reduced. However, electrical characteristics are not greatly affected but elements can perform normal operation.
On the other hand, in a case where the defective crystallization region RW divides the channel region CH transversely, that is, the defective crystallization region RW generated in the direction of the channel width is formed to have a length greater than the channel width, a moving path MNh of the TFT is blocked over the whole channel width by the defective crystallization region Rw even if the defective crystallization region RW is a part of the channel region CH. Therefore, the characteristics of the TFT are noticeably deteriorated.
The present invention provides a semiconductor device having a plurality of semiconductor elements formed on a substrate, some or all of the semiconductor devices having a channel region formed in a semiconductor film annealed by irradiation of a pulse laser beam, a channel width of the channel region being greater than a mutual pitch of the pulse laser beam irradiated by shifting a position, and the channel region being formed in such a manner that the direction of the channel width is not coincident with the directions of the major and minor axes of a region where the pulse laser beam is irradiated.
Furthermore, the present invention is characterized in that the directions of the sides of the substrate are almost the same as the directions of the major and minor axes of the region where the pulse laser beam is irradiated, and the direction of the channel width of the channel region is different from the directions of the sides of the substrate.
Alternatively, it is also possible to employ a structure in which the directions of the sides of the substrate are almost the same as the direction of the channel width of the channel region, and the directions of the major and minor axes of the region where the pulse laser beam is irradiated are different from the directions of the sides of the substrate.
With such a structure, even if a defective laser-annealed region formed in the semiconductor film with the same width as the pitch of the pulse laser beam is generated in the vicinity of the channel region of the semiconductor element, the channel region can be prevented from being occupied by the defective processed region over the whole channel width. Consequently, characteristics of the semiconductor element can be prevented from being deteriorated.
In the present invention, it is also possible to use a structure in which some semiconductor elements have a polycrystalline semiconductor film formed on the substrate by polycrystallizing an amorphous semiconductor by annealing using irradiation of a pulse laser beam, a channel region formed in an island region of the polycrystalline semiconductor film, and a gate electrode formed to overlap the channel region with an insulation film provided therebetween.
In another aspect of the present invention, a channel width W of the channel region, a pitch P of the pulse laser beam, and an angle xcex8 formed by the direction of the channel width of the channel region and the direction of the major axis of the region where the pulse laser beam is irradiated have a relationship satisfying Wxc2x7sin xcex8 greater than P.
Furthermore, it is also possible to apply a structure if a channel length of the channel region is set to L, a pitch P of the pulse laser beam and the angle xcex8 formed by the direction of the channel width of the channel region and the direction of the major axis of the region where the pulse laser beam is irradiated have a relationship satisfying Wxc2x7sin xcex8xe2x88x92L cosxc2x7xcex8 greater than P.
With such a structure where the defective treated region obtained by the annealing is formed in the vicinity of the channel region of the semiconductor element, the channel region can be reliably prevented from being occupied by the defective treated region over the entire channel width.
In yet another aspect of the present invention, if a channel width W of the channel region, a channel length L of the channel region, a pitch P of the pulse laser beam, and an angle xcex8 formed by the direction of the channel width of the channel region and the direction of the major axis of the region where the pulse laser beam is irradiated have a relationship satisfying Wxc2x7sin xcex8xe2x88x92Lxc2x7cos xcex8 greater than P, the channel region can be more reliably prevented from being occupied by a defective annealed region.
A further aspect of the present invention is directed to a semiconductor device having a plurality of semiconductor elements formed on a substrate, some or all of the semiconductor elements formed on a substrate, some or all of the semiconductor devices having a polycrystalline semiconductor film formed on the substrate by polycrystallizing an amorphous semiconductor by annealing using irradiation of a pulse laser beam, a channel region formed in an island region of the polycrystalline semiconductor film, and a gate electrode formed to overlap the channel region with an insulation film provided therebetween, the semiconductor device having a lightly doped drain structure, a channel width of the channel region being greater than a mutual pitch of the pulse laser beam irradiated by shifting a position, and the channel region being formed in such a manner that a direction of the channel width is not coincident with the directions of the major and the minor axes of a region where the pulse laser beam is irradiated.
Also in such a semiconductor element having a LDD structure, the channel region of the semiconductor device is formed to have the above-mentioned relationship with the pitch of the pulse laser beam. Consequently, the characteristics of the semiconductor device can be prevented from being deteriorated.
Furthermore, the present invention is characterized in that a channel width W of the channel region, a channel length L of the channel region, a length L1 of the lightly doped region, a pitch P of the pulse laser beam, and an angle xcex8 formed by the direction of the channel width of the channel region and the direction of the major axis of the region where the pulse laser beam is irradiated can have a relationship to satisfy Wxc2x7sin xcex8xe2x88x92(L+L1)xc2x7cos xcex8 greater than P.
By employing such a structure of the semiconductor device, where the defective treated region obtained by the annealing is formed in the vicinity of the channel region of the semiconductor element having the LDD structure, the channel region and the LD region which greatly affected element characteristics can be reliably prevented from being occupied by the defective treated region in the direction of the channel width.
A further aspect of the present invention is directed to a display device having the same characteristics as in the above-mentioned semiconductor device. The display device comprises, on a substrate, a plurality of first thin film transistors for supplying a display signal to corresponding pixels, respectively, and a plurality of second thin film transistors constructing a driver circuit for driving the first thin film transistors, the first and/or second thin film transistors having channel regions provided in polycrystalline semiconductor films formed on the substrate by polycrystallizing an amorphous semiconductor by annealing using irradiation of a pulse laser beam, some or all of the second thin film transistors having a channel width of the channel region which is greater than a mutual pitch of the pulse laser beam irradiated by shifting a position, and the channel region being formed in such a manner that the direction of the channel width is not coincident with directions of the major and minor axes of a region where the pulse laser beam is irradiated.
If characteristics of the second thin film transistors for driving the first thin film transistors corresponding to the pixels are deteriorated, the quality of the display is significantly affected than in a deterioration in characteristics of the first thin film transistors. Accordingly, the channel regions of the second thin film transistors are formed as described above so that they can be prevented from being occupied over the entire channel widths by the defective treated region obtained by the laser annealing. Thus, the characteristics of the second thin film transistors can be prevented from being deteriorated.
The display device according to the present invention can have a structure in which a channel width W of the channel region, a pitch P of the pulse laser beam, and an angle xcex8 formed by the direction of the channel width of the channel region and the direction of the major axis of the region where the pulse laser beam is irradiated have a relationship satisfying Wxc2x7sin xcex8xe2x88x92P. With such a structure, the characteristics of the second thin film transistors can be reliably prevented from being deteriorated.
A further aspect of the present invention is directed to a semiconductor device having a plurality of semiconductor elements formed on a substrate, some or all of the semiconductor elements having a channel region formed on a semiconductor film annealed by irradiation of a pulse laser beam, the channel region being formed by a plurality of channel region parts which are separated from each other and are electrically connected in parallel, and a sum of each of the channel widths of the channel region parts and a space between the channel region parts being greater than a mutual pitch of the pulse laser beam irradiated by shifting a position.
A further aspect of the present invention is directed to the semiconductor apparatus wherein the channel region parts are respectively separated in the directions of the channel widths.
Also in a case where the channel region of the semiconductor device is thus formed for the pitch of the pulse laser beam, the whole channel width of the channel region of the semiconductor device can be prevented from being occupied by the defective treated region obtained by the laser annealing. Thus, the characteristics of the semiconductor device can be prevented from being deteriorated.
A further aspect of the present invention is directed to a display device comprising, on a substrate, a plurality of first thin film transistors for supplying a display signal to corresponding pixels, respectively, and a plurality of second thin film transistors constructing a driver circuit for driving the first thin film transistors, the first and/or second thin film transistors having channel regions provided in polycrystalline semiconductor films formed on the substrate by polycrystallizing an amorphous semiconductor by annealing using irradiation of a pulse laser beam, some or all of the second thin film transistors having a channel region formed by a plurality of channel region parts which are separated from each other and are electrically connected in parallel, and a sum of each of the channel widths of the channel region parts and a space between the channel region parts being greater than a mutual pitch of the pulse laser beam irradiated by shifting a position.
If characteristics of the second thin film transistors for driving the first thin film transistors corresponding to the pixels as described above are deteriorated, the quality of display is more significantly affected than in a deterioration in characteristics of the first thin film transistors. The channel regions of the second thin film transistors are formed to have the above-mentioned relationship with the pitch of the pulse laser beam so that they can be prevented from being occupied over the whole channel widths by the defective treated region obtained by the laser annealing. Thus, the characteristics of the second thin film transistors can be prevented from being deteriorated.